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NASA-TM-108061 

A Study of Interior Landscape Plants 

for 
Indoor Air Pollution Abatement 

An Interim Report 



B. C. Wolverton, Ph.D. 
Principal Investigator 

National Aeronautics and Space Administration 

John C. Stennis Space Center 

Stennis Space Center, MS 39529-6000 



Willard L. Douglas, Ph.D. 
Research Chemist • 



Keith Bounds, M.S. 

Research Chemist 

Sverdrup Technology, Inc. 

John C. Stenn-is Space Center 

Stennis Space Center, MS 39529 

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BACKGROUND: 

In the previous report, dated October 1989, preliminary data on the 
ability of a group of common indoor plants to remove organic 
chemicals from indoor air was presented. The group of plants 
chosen for this study was determined by joint agreement between the 
National Aeronautics and Space Administration (NASA) and The 
Associated Landscape Contractors of America (ALCA) . 

PLANTS CHOSEN FOR SCREENING: 



Common Name: 



Scientific Name: 



Bamboo palm 

Chinese evergreen 

English Ivy 

Gerbera daisy 

Janet Craig 

Marginata 

Mass cane/Corn cane 

Mother- in-Law's tongue 

Pot mum 

Peace lily 

Warneckei 

Ficus 



Chamaedorea seifritzii 

Aalaonema modestum 

Hedera helix 

Gerbera Jameson ii 

Dracaena deremensis "Janet Craig" 

Dracaena marginata 

Dracaena massangeana 

Sansevieria laurentii 

Chrysanthemum mori folium 

Spathyphyllum "Mauna Loa" 

Dracaena deremensis "Warneckei" 

Ficus beniamina 



PRECEDING PAGE BLANK NOT FILMED 



In addition to this group of plants, several others have been used 
during the study. These include several plants in the philodendron 
family such as the heart leaf philodendron ( Philodendron 
oxycardium ) , the elephant ear philodentron ( Philodendron 
domesticum ) , the golden pothos ( Scindapsus aureus ) and the green 
spider plant ( Chlorophvtum elatum ) . These plants are being 
included in some tests because they represent the group of plants 
which were used in some of the original 'work done in this 
laboratory and therefore serve as a point of comparison between 
current and previous work. 

The chemicals chosen for study were benzene, trichloroethylene and 
formaldehyde. Although many other chemicals are commonly found in 
indoor atmospheres, these have been indicated as possible 
carcinogens or teratogens and are some of the more commonly found. 
The characteristics and sources of these chemicals in indoor air 
were described in the previous report. 

SUMMARY OF PREVIOUS RESULTS: 

The previous report shows the results of preliminary screening 
tests that were performed using Sensidyne-Gastec air sampling 
equipment. This equipment consists of detector tubes that are 
specific for different chemicals and a hand held pump to draw air 
through the tubes. When air containing the chemical is drawn 



through the tube, a reaction takes place and a color change occurs 
which is proportional to the concentration of chemical in the air 
sample. Table 1 lists the plants and chemicals not included in the 
October, 1988 report. This completes the initial screening of all 
plants on the ALCA list. 

CURRENT TESTING METHODS: 

For experiments previously reported, the concentrations of chemical 
were in the 15 to 20 part per million (PPM) range. Although this 
gave a good indication of which plants might be particularly suited 
to the removal of one or more of the chosen chemicals, it is far 
above the levels commonly found in indoor atmospheres. Therefore, 
shortly after issuing the previous report, we began to investigate 
removal of much lower concentrations (less thah 1 PPM) of chemical 
from the air. As the Sensidyne-Gastec equipment is not sensitive 
enough for testing these lower concentrations, a gas 
chromatographic (GC) method has been developed for analysis of both 
benzene and trichloroethylene (TCE) in the same sample. 
Formaldehyde cannot be determined by a GC method and an ultra 
sensitive chemical method is currently being evaluated for analysis 
of low levels of this chemical. As with all previous studies, 
plants were maintained in a healthy condition using Stern's 
Miracle-Grow fertilizer. 

All studies are being performed using the plexiglass chambers from 



previous experiments. For the benzene/TCE study currently 
underway, two chambers of similar size are being used, having 
volumes of 0.868 cubic meters and 0.694 cubic meters. Sampling is 
performed by withdrawing 200 mil of air through a glass tube 
containing Tenax adsorbent with a Sensidyne hand pump. The samples 
are analyzed promptly using a Supelco air desorption unit 
interfaced to a Hewlett-Packard Model 5890 gas chromatography, 
equipped with a Hewlett-Packard Ultra 2 capillary column and flame 
ionization detector. 

During past studies, the only controls used were chambers free of 
plants to test for loss of chemicals from leakage, and pots with 
potting soil without plants. It was then assumed that the removal 
of chemicals from the sealed chambers after making corrections for 
the potting soil could be attributed to the plant leaves. 

Another major change made for this study in, an effort to determine 
the exact mechanism involved in chemical removal was the 
defoliation of plants during the experiments and the coverage of 
potting soil with pea gravel using full plant foliage. 

To our surprise, we found with benzene that significant chemical 
removal appeared to be from the soil containing the plant roots. 
Thus, we began incorporating a test for this hypothesis into all 
experiments. Mature plants with full foliage were tested for one 
or more 24 hour period followed by testing of the same plants from 



which all of the foliage had been cut away, leaving only short 
stalks 1 to 2 inches in length protruding above the level of the 
potting soil. To determine if water vapor was important, some of 
the potting soil containers were saturated with water before 
conducting the tests. Water did not appear to be a major actor in 
chemical removal . 

Another major change made for this study was the analysis of plants 
that have been defoliated. Due to recent work) we began to suspect 
that the plant leaves were not solely responsible for removal of 
organics from the air. Thus, we began incorporating a test for 
this hypothesis into all experiments. Mature plants with full 
foliage were tested for one or more 24 hour period (identical to 
methods previously used) , followed by testing of the same plants 
from which all of the foliage had been cut away, leaving only short 
stalks 1 to 2 inches in length protruding above the level of the 
potting soil. Plants were also tested with the potting soil 
covered with pea gravel. 

The general protocol followed for these tests is summarized as 
follows: 

1. For each test, two healthy individuals of the plant 
species to be tested were used. One individual was 
placed into each of two chambers. 



■2 . The chambers were sealed and a mixture of benzene/TCE 
injected into each. 

3. After a short equilibration period to allow for complete 
volatilization and circulation of the chemicals inside 
the chamber, two replicate samples were withdrawn from 
each chamber. These samples were analyzed without delay 
on the GC. If the two samples drawn from a single 
chamber did not replicate within approximately 10%, two 
more replicates were drawn and analyzed. 

4. The plants were left overnight in the sealed chambers. 
In some cases a sample was drawn 4 to 6 hours after 
injection of chemical. However, in most cases, only a 
final sample, drawn approximately 21 to 22 hours 
following injection, was collected. As with the initial 
sample, replicates were withdrawn, from each chamber and 
analyzed as described above. 

5. At the end of the 24 hour testing period, the chambers 
were opened and the plants removed. All of the foliage 
was cut away from the plant 1 to 2 inches above the 
surface of the potting soil. 

6. The chambers remained open for approximately one hour, 
during which time a good circulation of air was 



maintained in them to remove any remaining organics prior 
to resealing. 

7. The defoliated plants were placed back into the chambers 
and the chambers were resealed. 



8. Initial and final sampling was performed as described 
above . 



Although the above outline indicates- the general protocol followed, 
variations occurred in most actual trials. In all tests, however, 
two individuals of the same species were tested and the foliage 
was completely removed from at least one of these two plants. In 
several trials, the two plants were tested for two or three days 
with full foliage, following testing for a similar period with the 
potting soil covered with pea gravel. Tests were then conducted 
with uncovered potting soil after removal of foliage. 

During the course of these experiments, leak tests on sealed, empty 
chambers were periodically conducted to affirm that the chambers 
did not leak during the course of the experiments. 

RESULTS: 

It can be seen from Table 1 and earlier reports that for virtually 
all plants tested, the reductions in benzene and formaldehyde are 



significant. The most interesting observation from data shown in 
Table 2 is that the mean removal of benzene by the defoliated 
marginata is greater than the removal by plants with full foliage. 
This suggests that the plant roots and their associated 
microorganisms are the major pathway for chemical removal, at least 
in this study. This phenomenon cannot be fully explained at this 
writing. We are continuing to study this from various aspects to 
try to determine why it occurs. Microbial studies have been 
implemented in an effort to better understand this phenomenon. 

Figures 1 and 2 also demonstrates the efficiency of plant/activated 
carbon filters for removing benzene and trichloroethylene from 
contaminated air inside sealed chambers. The cfm rate of the fan 
used is a major controlling factor in the speed in which a room can 
be cleaned of smoke and toxic chemicals. The. small 8" pot system 
used in Figure 1 had a motor fan rating of 15 cfm free air flow. 

DISCUSSION: 

As in previously reported studies, these results indicate that 
plants can play a major role in removal of organic chemicals from 
indoor air. The work reported herein confirms that plant systems, 
and not the potting soil itself, are responsible for removing most 
of these chemicals. However, it now appears that the part 
microorganisms and plant roots play may be more important in the 
removal of chemicals than was previously believed. This opens a 



broad new avenue that will be investigated and discussed in depth 
in the final report. 

It is also interesting to note in our studies, that for the soil 
to be highly effective in removing indoor air pollutants, plants 
must be growing in this soil. Therefore, the plant is very 
important in removing indoor air pollution either directly through 
its leaves or indirectly through the root/soil pathway. For 
removal of high concentrations of chemical^ and/or smoke from 
inside buildings it is desirable to have an integrated system using 
potting plants and one or more activated carbon/plant filtration 
systems . 



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FIGURE 1. REMOVAL OF LOW CONCENTRATIONS 

OF BENZENE AND TRICHLOROETHYLENE FROM 

THE AIR INSIDE SEALED EXPERIMENTAL 

CHAMBERS USING GOLDEN POTHOS IN AN 

8-IN. ACTIVATED CARBON FILTER SYSTEM. 



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FIGURE 2. REMOVAL OF HIGH CONCENTRATIONS 

OF BENZENE AND TRICHLOROETHYLENE FROM 

THE AIR INSIDE SEALED EXPERIMENTAL 

CHAMBERS USING GOLDEN POTHOS IN AN 

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